Art. 2. 



PETROLOGY AT GOOSE CREEK SHANNON. 



81 



in the pegmatitic rocks, both the normal diabase pegmatite and the 

 albitic rocks where it forms grains and crystals in porous spots or 

 small miarolitic cavities. It is also of fre- 

 quent occurrence embedded in diopside in 

 diopside-filled seams. / i> I \ 



SPHALERITE. 



How rare sphalerite is may be adduced 

 from the fact that only a single grain of 

 this zinc sulphide was found in all of the 

 specimens collected. This grain, which 

 was about 2 mm. in diameter, possessed 

 good cleavage and was vivid greenish yel- 

 low in color. It was embedded in a broad 

 cleavage surface of apophyllite and was 

 obviously contemporaneous with the 

 apophyllite. 



PARAGENESIS. 



The minerals observed in the secondary 

 deposits in the veins occur, usually, in 

 groups of from one to three or four in any 

 given specimen and the relative ages can 

 only be adduced by a process of fitting 

 together the evidence derived from a 

 study of a large number of specimens. 



Overlapping sequences were not proven 

 to occur and it is assumed, tentatively, 

 that all of the minerals belong to a sin- 

 gle series. This series, as well as it can 

 be worked out, is as follows, beginning 

 with the earhest cavity-filling mineral; 



Fig. 29.— Apophyllite showing com- 

 bination OF PYRAMID WITH FACES 

 OF FOUR PRISMS. 



Albite. 



Chlorite. 



Hornblende (asbestiform) 



Epidote (hour-glass). 



Axinite. 



Quartz. 



Prehnite. 



8. Datohte. 



9. Chabazite. 



10. Stilbite. 



11. Laumontite. 



12. Opal (hyalite). 



13. Apophyllite. 



14. Calcite. 



The position of albite is rather definitely fixed by its occurrence 

 underlymg both chlorite and hornblende. 



Chlorite is in most cases a very early mineral although it may also 

 occur as a later deposit. 



94110—24- 



